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United States Patent |
6,190,389
|
Wellisz
,   et al.
|
February 20, 2001
|
Bone alignment and fixation device and method
Abstract
This invention concerns a device, and instruments for its insertion, that
aligns two sections of bone and fixates the two sections to one another.
The alignment feature and the fixation feature are typically independent,
but they are incorporated into one device. The device is particularly well
adapted to the alignment and fixation of a fragment of cranial bone with
the remainder of the cranium. The device can be applied to a cranial bone
fragment, and it allows the bone fragment to be aligned with the outer
cortex of the cranium; prevents the bone fragment from entering the
cranial cavity; and if desired, fixates the bone fragment to the cranium.
Inventors:
|
Wellisz; Tadeusz Z. (Los Angeles, CA);
Hohenstein; Eric V. (Los Angeles, CA)
|
Assignee:
|
Bioplate, Inc. (Los Angeles, CA)
|
Appl. No.:
|
435646 |
Filed:
|
November 9, 1999 |
Current U.S. Class: |
606/69; 606/72; 606/73 |
Intern'l Class: |
A61B 017/80 |
Field of Search: |
606/69,70,72,75,86,104,151
29/243.56
411/61,508
|
References Cited
U.S. Patent Documents
3220081 | Nov., 1965 | Rector.
| |
3716050 | Feb., 1973 | Johnston | 606/72.
|
4936844 | Jun., 1990 | Chandler et al. | 606/69.
|
5487741 | Jan., 1996 | Maruyama et al.
| |
5501685 | Mar., 1996 | Spetzler.
| |
5549620 | Aug., 1996 | Bremer.
| |
5669912 | Sep., 1997 | Spetzler.
| |
5674222 | Oct., 1997 | Berger et al. | 606/69.
|
5810822 | Sep., 1998 | Mortier | 606/69.
|
5868746 | Feb., 1999 | Sarver et al. | 606/69.
|
5916217 | Jun., 1999 | Manthrop et al.
| |
5941878 | Aug., 1999 | Medoff.
| |
5953803 | Sep., 1999 | Hahn | 29/243.
|
Foreign Patent Documents |
WO 97/42912 | Nov., 1997 | WO.
| |
Primary Examiner: Philogene; Pedro
Attorney, Agent or Firm: Haefliger; William W.
Claims
We claim:
1. A clip to inter-connect primary and secondary bone zones having edges,
comprising in combination:
a) a tab to extend over a surface of the secondary bone zone, above a level
defined by that surface, and
b) a first projection carried by the tab and configured to penetrate the
primary bone zone at the edge thereof, and below said first level.
2. The combination of claim 1 including an extension of the tab projecting
below said first level, said extension carrying the first projection.
3. The combination of claim 2 including a second projection carried by the
tab and configured to engage the secondary bone zone at the edge thereof,
and below said surface level.
4. The combination of claim 3 wherein the second projection is carried by
the tab extension.
5. The combination of claim 2 wherein said tab has the form of a plate that
extends forwardly and then downwardly to define said extension, said first
projection extending generally parallel to the tab and forwardly from a
part of the tab extension below said level.
6. The combination of claim 1 wherein said first projection has a sharp
terminal to enable penetration of bone marrow.
7. The combination of claim 3 wherein said first projection projects in a
direction generally away from said second projection.
8. The combination of claim 4 wherein said second projection has a sharp
terminal to enable penetration of diploe.
9. The combination of claim 1 wherein said second projection extends at an
acute angle relative to said extension, and toward said tab.
10. The combination of claim 2 including at least one of the following: i)
a through hole in the tab to receive a fastener, and ii) a through hole in
the extension, to receive a fastener.
11. The combination of claim 1 including another second projection carried
by the tab in sidewardly spaced relation to the first mentioned second
projection, and configured to engage the secondary bone zone at the edge
thereof, and below said level.
12. The combination of claim 11 wherein each said second projection has a
sharp terminal to enable penetration of bone tissue, said sharp terminals
being relatively divergent.
13. The combination of claim 12 wherein each second projection extends back
upwardly at an acute angle toward the tab, where said angle is about
30.degree..
14. The combination of claim 3 including said primary bone zone penetrated
by a tip of said first projection, and said secondary bone zone engaged by
a tip of said second projection.
15. The combination of claim 1 including a cranial bone flap defining said
primary bone zone.
16. The combination of claim 15 including multiple of said clips having
said first projections penetrating the primary bone zone below a surface
defined by the flap.
17. The combination of claim 3 wherein said second projection is a barb.
18. The combination of claim 17 wherein there are two of said barbs angled
upwardly, and located on zones defined by said tab extension, said zones
projecting laterally oppositely relative to said first projection.
19. The combination of claim 18 including attachment wings defined by said
extension.
20. The method of using a clip to interconnect primary and secondary bone
zones having edges, the clip comprising
a) a tab to extend over a surface of the secondary bone zone, above a level
defined by that surface, and
b) a first projection carried by the tab and configured to penetrate the
primary bone zone at the edge thereof, and below said first level, said
method including the steps
i) causing the first projection to penetrate said primary bone zone,
ii) and then locating the tab to extend over said surface of the secondary
bone zone, and attaching the tab to said surface.
21. The method of claim 20 including a second projection carried by the tab
and configured to engage the secondary bone zone at the edge thereof, and
below said surface level, the method including displacing the clip and
said second projection to engage the secondary bone zone at the edge
thereof, below said surface level.
22. The method of claim 20 wherein said step i) includes pushing the clip
toward said primary bone zone to effect push-in penetration of the first
projection into said primary bone zone.
23. The method of claim 22 including orienting the second projection at the
edge of the secondary bone zone to resist reverse displacement of the clip
in an upward or opposite direction relative to the secondary bone zone.
24. The method of claim 23 including effecting penetration of the edge of
the secondary bone zone by the second projection in an angular direction
toward the tab.
25. A cranial clip comprising, in combination
a) a clip having a support plate,
b) a flange integral with the plate and extending away from the plate,
c) at least one push-in tang integral with and protruding from the flange
and extending generally parallel to the plate,
d) said tang having a sharp tip to be pushed into cranial soft bone tissue
proximate an edge of the skull.
26. The combination of claim 25 including an installation tool interfitting
the clip support plate and flange, for forwardly pushing and guiding the
clip, as the tang penetrates said soft bone tissue.
27. The combination of claim 25 wherein the clip flange has at least one
integral ring, and an aligner on the ring.
28. The combination of claim 26 wherein the tool has at least one alignment
bar projecting forwardly at the level of the top plate, for guided
engagement with the top of the skull.
29. Apparatus to prevent a bone fragment from entering the cranial cavity,
during positioning of said fragment at an opening in the cranium,
comprising
a) a carrier for the bone fragment, and
b) an aligner on the carrier to engage a surface or surfaces of the cranium
during positioning of the bone fragment relative to said cranial opening.
30. The apparatus of claim 29 wherein the aligner has left and right slide
surfaces to engage the cranial outer surface, as the aligner and bone
fragment are moved forwardly.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to the alignment and fixation of bone
segments as required for appropriate bone healing, for example after
fracture or surgical intervention, and specifically to a device, and the
tools needed to install the said device, for the alignment and fixation of
cranial bone fragments.
In cases of bone fragmentation where bone fixation is desired, the
appropriate alignment of the bone is also a desired result. This is
especially true in the cranium, where bone fragmentation can occur as a
result of trauma, congenital deformity, or of surgical intervention. In
the field of neurosurgery, cranial bone fragments are frequently cut and
removed to create defects to allow for access into the cranial cavity and
the brain.
The bony cranium is generally regarded to have two surfaces: the outer
surface which is characterized by the outer cortex of the bone and is
adjacent to the scalp and soft tissue; and the inner surface which is
characterized by the inner cortex of the bone and which is adjacent to the
cranial cavity and the brain. Between the inner cortex and the outer
cortex, which are dense layers of bone, lies the diploe which generally
consists of soft bone and bone marrow. When a bone fragment is created, a
cut between the bone fragment (the primary bone zone) and the remainder of
the cranium (the secondary bone zone) is present.
Several methods of alignment and fixation of primary and secondary bone
zones are known. Traditional techniques involve the use of several pieces
of filament, such as wire, that are tied after being threaded through
holes drilled obliquely through the outer cortex to the cut surface of
both bone zones. Precise alignment of the two zones can be difficult and
the technique can be cumbersome.
Commonly, the zones of bone can be aligned and fixated with a system of
plates and screws (U.S. Pat. Nos. 5,372,598; 5,413,577; and 5,578,036). A
plate made of metal or other substance can be fixated to the outer cortex
of the primary bone zone with screws whose penetration of the bone can be
limited to the outer cortex. With three of more plates attached to the
primary bone in such a way that the plates protrude beyond the edges of
the primary bone zone, the primary bone zone can be introduced into a
defect and aligned to the outer cortex of the secondary bone zone without
danger of the primary bone zone falling too deeply into the defect in the
secondary bone zone and exerting pressure on the underlying tissue such as
the brain. Fixation can then be achieved by employing additional screws
fixating the plates to the outer cortex of the secondary bone zone. Plates
and screws systems allow for the alignment and fixation of the zones,
while preventing the primary bone zone from falling below the level of the
secondary bone zone without actually introducing a component of the device
below the secondary bone zone. A plate with a spring clip extension has
been described (U.S. Pat. No. 5,916,217). Plate and screw systems can be
expensive and time consuming to use.
Devices that align the two bone zones by way of compressing them between
the two disks positioned along the inner and outer cortex have been
described. (Foreign Patents: DE 19603887C2, DE 19634699C1, DE 29812988U1,
EP 0787466A1.) A pin connects the two disks aligning and securing two bone
zones. These devices introduce foreign material that is left below the
inner cortex, and they do not protect the underlying tissue from
compression during the installation procedure.
Devices that fixate bone zones using friction forces created by a cam
without a component that extends below the inner cortex are known and
described (Patent DE 19634697C1). These devices also do not protect the
brain from compression during the installation procedure.
Intramedulary pins are well known in the orthopedic fields for alignment of
long bones. Such pins have also been described for cranial fixation (U.S.
Pat. No. 5,501,685); however, the bone zones can not be aligned in three
dimensions with this technique.
There is a need for an alignment and fixation device that is simple and
rapid to use, versatile, and ultimately cost effective.
OBJECTS OF THE INVENTION
The object of the invention is to provide a device and instruments for its
use that aligns the one cortex of a primary zone with one cortex of a
secondary bone zone without extending to the opposing cortex, and which
fixates the bone zones to each other. When used in the field of
neurosurgery, the device is applied to the primary bone zone and it aligns
the outer cortex of the primary bone zone with the outer cortex of the
secondary bone zone; it prevents the primary bone zone from entering the
cranial cavity; and it provides fixation of the two bone zones. The
alignment feature can be used independently from the fixation feature. An
example of the use of the alignment feature is in the replacement of a
cranial bone fragment which will be held in place by the tissue forces of
the scalp, which allows for the bone fragment to be elevated away from the
cranial cavity in cases where brain swelling occurs. Fixation can also be
applied to attach the alignment device to the bone, using elements alone
or in combination such as filaments, screws, rivets, pins, clips, cams,
friction or adhesives. The alignment aspect of the invention can also be
applied to situations where it is desired to offset the alignment of the
bone fragment to the adjacent bone such as where the object is to create a
more prominent chin by cutting the bone of the chin and advancing the bone
fragment.
The fixation feature of the invention is likewise independent from the
alignment feature. The fixation feature of the device relies on the
principle that the device is fixated to the primary bone zone and the
fixation feature grips the secondary bone zone by means of spring loaded
tab or hook elements engaging the soft areas of the medullary space,
irregularities along the cut surface, or a slot cut into the cut surface
of the secondary bone zone.
SUMMARY OF THE INVENTION
The invention provides an improved clip meeting the above need or needs.
As will be seen the preferred clip is configured to interconnect primary
and secondary bone zones having edges spaced apart by a gap, the clip
comprising
a) a tab such as a small plate to extend over a surface of the secondary
bone zone, above a level defined by that surface, and
b) a first projection carried by the tab and configured to penetrate the
primary bone zone at the edge thereof, and below said surface level.
As will be seen, a second projection may be provided and carried by the tab
and configured to engage the secondary bone zone at the edge thereof, and
below said surface level.
It is another object to provide an extension of the tab projecting below
said first level, that extension carrying the first projection, and also
the second projection if it is provided. In this regard, the second
projection is typically located beneath the tab; and the first projection
extends generally parallel to the tab and forwardly from a part of the tab
extension below said surface level, and it preferably has a sharp terminal
to enable penetration of diploe.
A further object is to provide the second projection to have a sharp
terminal, and to extend at an angle toward the tab, in order to resist
removal relative to the secondary bone zone.
Yet another object is to provide another second projection carried by the
tab in sidewardly spaced relation to the first mentioned second
projection, and configured to engage the secondary bone zone at the edge
thereof, and below said surface level.
An additional object is to provide a plate or flap defining the primary
bone zone, and to provide multiple of the clips having their first
projections penetrating the primary bone zone at different edges thereof,
below a surface defined by the plate or flap.
The method of using the clip as referred to includes the steps
i) causing the first projection to penetrate the primary bone zone,
ii) and then locating the tab to extend over said surface of the secondary
bone zone, and attaching the tab to that surface.
As will be seen, the step i) preferably includes pushing the clip toward
the primary bone zone to effect push-in penetration of the first
projection into said primary bone zone. The method may further include
providing a second projection carried by the tab and configured to engage
the secondary bone zone at the edge thereof, and below said surface level,
the method including displacing the clip and said second projection to
engage the secondary bone zone at the edge thereof, below said surface
level. An additional step includes displacing the clip in a direction to
effect scraping of the edge of the secondary bone zone by the second
projection, the second projection oriented to resist reverse displacement
of the clip in an upward or opposite direction relative to the secondary
bone zone. In this regard, the method may include effecting penetration of
the edge of the secondary bone zone by the second projection in an angular
direction toward the tab.
These and other objects and advantages of the invention, as well as the
details of an illustrative embodiment, will be more fully understood from
the following specification and drawings, in which:
DRAWING DESCRIPTION
FIG. 1 is a perspective view showing a bone flap fixated on a skull,
employing fixation clips;
FIG. 2 is an enlarged perspective view showing a clip employing the
invention;
FIG. 3 is a top plan view of the FIG. 2 clip;
FIG. 4 is an end view of the clip taken on lines 4--4 of FIG. 3;
FIG. 5 is a side elevational view taken on lines 5--5 of FIG. 3;
FIG. 6 is a plan view of a clip blank in one plane, prior to deformation to
FIG. 2 configuration;
FIG. 7 is a section showing the FIG. 1 clip attached to primary and
secondary bone zones;
FIG. 8 is a perspective view showing clip attachment to a primary bone
zone;
FIG. 9 shows multiple clips attached to opposite edges of a bone flap
defining primary bone zones;
FIG. 10 shows the clips installed in a skull opening;
FIG. 11 is a perspective view like FIG. 2, showing a modified clip;
FIG. 12 is a perspective view like FIG. 11 showing another modified clip;
FIG. 13 is a perspective view similar to FIG. 8, and showing attachment of
a clip of FIG. 11 form, to a primary bone zone, such as a bone flap;
FIG. 14 is a section taken through a cranial bone flap, having two FIG. 11
type clips attached at opposite edges, and positioned for clip attachment
to secondary bone zone sections;
FIG. 15 is a perspective view showing a cranial bone flap having four FIG.
11 type clips attached, at its four edges;
FIG. 16 is a perspective view of a further modified clip, of FIG. 2 type;
FIG. 17 is a perspective view of a tool usable in conjunction with the FIG.
16 clip, to effect penetration of a clip projection into a primary bone
zone;
FIG. 18 shows use of a barb;
FIG. 19 is a top plan view of a further modified clip using a barb;
FIG. 20 is an end view taken on lines 20--20 of FIG. 19;
FIG. 21 is a side elevational view taken on lines 21--21 of FIG. 19; and
FIG. 22 is a plan view of a clip blank in one plane, prior to deformation
to FIG. 19 configuration.
DETAILED DESCRIPTION
Referring to FIGS. 2-5 and 7, the illustrated and preferred clip 10 is
configured to interconnect primary and secondary bone zones 11 and 12
having opposed and spaced apart edges 11c and 12c. A cut or gap 13 is
formed between the opposed edges of the primary and secondary bone zones.
Diploe is shown at 15 between the top and bottom surfaces 11a and 11b of
zone 11; and at 16 between the top and bottom surfaces 12a and 12b of zone
12. As also seen in FIG. 1, primary bone zones 11 may be defined by bone
flap 17; and secondary bone zones 12 may be defined by skull 18 and its
zone extents at 12 opposing zones 11. In the adult, cranial bone or skull
averages 7 mm in thickness, but varies between 3 and 12 mm.
The clip 10, which is preferably metallic includes the following
a) a tab 20 to extend over a surface 12a of the secondary bone zone 12,
above surface level;
b) a first projection 21 carried by the tab and configured to penetrate the
exposed diploe of the primary bone zone 11 at the edge 11c of that zone
(and typically into diploe 15);
c) and at least one second projection 22 carried by the tab and configured
to engage (for example gouge into) the exposed diploe of the secondary
bone zone 12 at its edge 12c, below the level of surface 12a.
In the example, two such second projections are provided, as is clear from
FIGS. 4 and 6, and they are located at opposite sides of a lengthwise
plane 23 bisecting the clip, including projection 21. See FIGS. 4 and 6.
Such projections are equally spaced from plane 23, as indicated by
dimensions D.sub.1, seen in FIG. 4. The projections 21 and 22 have legs
21a and 22a, and their terminals are sharpened at 21b and 22b, to
facilitate penetration of the diploe zones, as seen in FIG. 7. Leg 21a and
projection 21 extend forwardly in direction 24 from a tab downward
extension 20a; and projection 22 extends back upwardly at an approximate
angle of 30.degree. C. toward the underside of the tab 20. Note that leg
22a extends from tab extension 20a and is U-shaped. A bend is formed at
22d. Projections 22 may also diverge laterally oppositely, as seen in FIG.
4, to provide greater stability of the plate or flap 17, as in FIG. 10
installed condition. Four edges 11c of that flap are seen in FIGS. 1 and
9, and corresponding four edges 12c of the skull face the flap edges and
receive penetration of the stabilizing clip projections 22, as described.
The method of use of the clip or clips includes the following steps:
i) causing the first projection or projections 21 to penetrate the primary
bone zone or zones;
ii) and then causing the second projection or projections 22 to grip the
secondary bone zone at the edge thereof.
Step i) includes pushing the clip 10 relatively toward the edge 11c of the
primary bone zone 11, as in direction 30 seen in FIG. 8. This effects
push-in penetration of the first projection 21 into the bone zone 11, as
for example into diploe 15. Push-in is typically completed when bent down
tab extension 20a closely approaches and/or engages edge 11c of the
primary bone zone 11 defined by the plate or flap 17. Four such pushed-in
clips are seen in FIG. 9, the clips located in opposed pair positions, at
four sides of the 17. Each tab 20 has a through hole 40 drilled or formed
therein to receive a fastener such as a retention screw, indicated at 41
in FIG. 5, to penetrate and attach to the skull proximate the secondary
bone regions.
The step ii) preferably also includes displacing the clip in a direction
(typically relatively downwardly toward the skull to bring 21, 22, and 20a
into gap 13 as seen in FIG. 7) to effect scraping of the edge 12c of the
secondary bone zone 12 by the tip of the angled second projection. That
projection is oriented, i.e. angled, to resist displacement of the clip in
an upward or opposite direction, relative to bone zone 12. For example,
attempted upward and outward displacement would increase the "gouge-in"
movement of the second projection, into the diploe 16.
Note further that the installed spacing d.sub.2 of the bone zone edges 11c
and 12c is slightly less than the spacing d.sub.3 as measured from the
sharp terminal of the projection 22 to the surface 32 of the tab extension
facing the edge 11c. The width d.sub.2 of gap 13 between 11c and 12c is
slightly less than the dimension d.sub.3, i.e.
d.sub.2 <d.sub.3,
to provide a desirably tight installation of plate 17 into the
corresponding skull opening.
In FIG. 3 note angularity .beta. of the sharpened taper of projection 21,
where .beta. is approximately 67.degree., and the through opening 43 in
tab extension 20a to receive a fastener 44 (if used to attach extension
20a to 11.
Projections 22 can resiliently deflect, slightly to accommodate the
multiple clips to the gaps 13 between 11 and 12, as during plate or tab
downward installation, as seen in FIG. 10.
Reference is now made to the modified clip 110 of FIGS. 11 and 14. It
includes:
a) a tab or plate 120 to extend over a surface 112a of secondary bone zone
or zones 112 (see FIG. 14), above a level defined by that surface; and
b) a first projection 121 carried by the tab 120, and configured to
penetrate the edge of exposed diploe 111a of primary bone zone 111, below
the levels of tab 120 and surface 112a.
The projection or tang 121 has a leg 121a, and its forward terminal is
sharpened at 121b to facilitate penetration into the bone marrow zone, as
seen in FIG. 14. Leg 121a extends forwardly from a tab downward extension
120a in the form of a flange. The method of use of the clip 110 includes
the following steps:
i) causing the projection 121 to penetrate the primary bone zone, such as
into diploe, (see FIG. 13); and
ii) locating the tab 120 to extend over the surface 112a of the secondary
bone zone, as in FIG. 14 for example, and attaching the tab to that
surface, one mode of attachment being by use of a screw seen at 150 in
FIG. 14, to penetrate through a hole 151 in tab 120, and into secondary
bone zone 112.
FIG. 14 shows two such clips 110 attached to opposite edges 111b and 111c
of a primary bone zone 111, such as a flap removed from the skull. When
the flap is attached to the skull, as into opening 130, the tabs 120 are
attached to the upper surfaces 112a of the skull, at opposite sides of the
opening. FIG. 15 shows four such clips attached to the flap 111, at four
edges 111b-111e.
FIG. 12 illustrates a modified clip 210, having elements 220, 220a, 221,
221a and 221b, like corresponding elements of clip 110. Extension 120a in
FIG. 11 has two laterally spaced legs 120a' and 120a" that extend
downwardly below the level of projection 121, and projection 121 has flat
upper and lower surfaces; whereas in FIG. 12 the extension lower extent
220a' is laterally continuous, and projection 221 is cylindrical, and
tapers at its forward end.
A further modified clip 250 is shown in FIG. 16, and has elements like
those of clip 10, as viewed in FIGS. 2-7. Such corresponding elements are
given the same numbers. Also, the clip downward extension 20a has left and
right wings 20a' and 20a".
FIG. 17 shows a hand tool 80 to receive the FIG. 16 clip in position for
forward, push-in attachment to bone zone 11, as described. Tool 80 has a
body 81, with a top recess 82 to fit the tab 20. Forward facing surface 83
engages and positions the clip downward extensions 20a and its two wings
20a' and 20b'. Tool pins 84 and 85 closely fit into holes 86 and 87 in
those two wings, for alignment. Aligners in the form of alignment bars 87
and 88 projecting forwardly from body 81 ride onto the top surface 11a of
the flap 11, prior to penetration of the projection 21a into the marrow
15, so that the proper level of the projection 21 relative to top surface
11a is established. A tool handle appears at 89, and facilitates forward
pushing of the tool and clip, and retraction of the tool, off the clip
after its push-in assembly to the flap. In this way, accurate assembly is
rapidly achieved.
The clips as disclosed herein may consist of metal or plastic (synthetic
resin) material. One desirable metal is titanium.
Clips 10, 110, and 210 may be inverted, for alternate installations
relative to the bone zones.
Referring to FIGS. 19-22, the illustrated views of modified clip 200
correspond to views 3-6 of clip 10.
The clip 200, which is preferably metallic, includes the following:
a) a tab 220 to extend over a surface 212a of the secondary bone zone 212
above surface level;
b) a first projection 221 carried by the tab and configured to penetrate
the exposed diploe of the primary bone zone 211 at the edge 11c of that
zone (and typically into diploe 215);
c) and at least one second projection such as barb 222 carried by the tab
and configured to engage (for example gouge into) the exposed diploe 216
of the secondary bone zone 212, below the level of surface 212a.
In the example, two such second projections or barbs 222 are provided, as
is clear from FIGS. 20 and 22, and they are located at opposite sides of a
lengthwise plane 223 bisecting the clip, including projection 221. One
such barb is seen in FIG. 18. Such projections are equally spaced from
plane 223, and are formed in lower portions 222a of 220a, with adjacent
through openings 222a'. The projection 221 has a leg 221a, and its
terminal is sharpened at 221b, to facilitate penetration of the bone zone
215, as seen in FIG. 21. Leg 221a and projection 221 extend forwardly from
a tab downward extension 220a; and projection or barb 222 extends back
upwardly at an acute toward the underside of the tab 220. Note that
projection 222 extends from tab lower extension 220a and is U-shaped. A
bend is formed at 222d.
Side wings 240 and 241 integral with downward extension 220a contain
through openings 243 to receive fasteners (if used) to attach to 221.
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